Fuel Efficiency When Coasting

Motorist

Is it more economical on fuel to shift into neutral and coast, or is it better to shift up to the highest gear in your car.

foggy_lad

it is illegal to coast because you are not in control! The best thing to do is to change to the gear that best suits the speed you are travelling.

Cookie_Monster

Motorist wrote: »

Is it more economical on fuel to shift into neutral and coast, or is it better to shift up to the highest gear in your car.

in a modern car, no. if in neutral the engine needs to be fed petrol to tick over. if a gear is engaged the motion of the car keep the engine turning and no petrol is allowed into the cylinders saving fuel

Pottler

foggy_lad wrote: »

it is illegal to coast because you are not in control! The best thing to do is to change to the gear that best suits the speed you are travelling.

Really? Go on, Really? Do you get points and fines and stuff? How do they go about prosecuting you, is it based on a Gards hunch? "I clearly saw the accused coasting your honour, I could sense it so I could".

Gumbo

Pottler wrote: »

Really? Go on, Really? Do you get points and fines and stuff? How do they go about prosecuting you, is it based on a Gards hunch? "I clearly saw the accused coasting your honour, I could sense it so I could".

Witty comments doesnt make it legal, its still illegal in this country.

challengemaster

kceire wrote: »

Witty comments doesnt make it legal, its still illegal in this country.

I'd love to see the law on that one

2 stroke

I don't know if it is actualy illegal to coast, but its against the rules of the road. When 1 driver decides to drive by his own set of rules it often leads to disaster.

CiniO

kceire wrote: »

Witty comments doesnt make it legal, its still illegal in this country.

Links please...

CiniO

foggy_lad wrote: »

it is illegal to coast because you are not in control!

Not in control of what?

challengemaster

2 stroke wrote: »

I don't know if it is actualy illegal to coast, but its against the rules of the road. When 1 driver decides to drive by his own set of rules it often leads to disaster.

Coasting isn't mentioned anywhere in the rules of the road. We're all taught it's bad driving practice by driving instructors, but it's nowhere in road traffic act or in the rules of the road, which is, by the way, an interpretation of the road traffic act that is easy to read for your every day person

The purpose of the Rules of the Road is to save lives and prevent injury on our
roads. The rules apply to all road users: drivers, pedestrians, motorcyclists, horse
riders and cyclists.
The rules are written in plain English to encourage good behaviour on the road.
The rules ask us to take personal responsibility for our use of the road.
The Rules of the Road have been designed in an easy to read format. It is your
responsibility to read the rules and know them. At the back of the book is a
Glossary that explains some of the terms used. The rules are also published in
Irish.
The rules comply with and reflect the Road Traffic Law as at 31 December 2009.
Where planned changes in the law are known with certainty a comment is
included in the appropriate section to ensure the content reflects them. It will
be important to check the relevant section of the Road Safety Authority web site
www.rsa.ie for updates.
We can save lives and prevent injury by changing our behaviour. Reading these
rules and applying them will help achieve this goal.
It’s our responsibility.
It’s our choice.

2 stroke

Looks like you have me but I'm certain it used be in the old rules of the road book.

CiniO

2 stroke wrote: »

Looks like you have me but I'm certain it used be in the old rules of the road book.

I have this book (one issued in 1997 AFAIR) but it's at my parents house so I'll be able to check it only in few months when I'll be there.

However even if it was in the book, it could be as a good advice, because it was never in the Law.

WallyGUFC

Cookie_Monster wrote: »

in a modern car, no. if in neutral the engine needs to be fed petrol to tick over. if a gear is engaged the motion of the car keep the engine turning and no petrol is allowed into the cylinders saving fuel

How about a 99 Astra?

wonski

It is not illegal nor legal. I don't think there is a country in the world that would have to put this in their legislations.
Normally coasting isn't dangerous at all, but i would not go downhill through the corner at any speed in neutral. Power at the wheels helps a lot. Also there are emergency situations where you may need to accelerate rather than stop...
It is bad driving practice, but can't see a problem when most people do it only at approach (junctions, parkings etc)
No saving of fuel too, as someone mentioned any car with fuel injection will use close to none petrol when foot is off the gas (even 99 Astra). The difference when coasting wouldn't be that much too.

shedweller

kceire wrote: »

Witty comments doesnt make it legal, its still illegal in this country.

As is going over 120kph on the motorway but i don't see anyone complaining about that.

Cookie_Monster

wonski wrote: »

It is not illegal nor legal.

what is it then?

wonski

Cookie_Monster wrote: »

what is it then?

It is bad practice, as is changing your gear to late, or for example slow progress on road, or driving under the limit. Some posters here fail to see that if something can lead to fail driving test, it does not necesarily makes it illegal.

Cookie_Monster

wonski wrote: »

It is bad practice

that it may be but it still has to be either legal or not...

wonski

Cookie_Monster wrote: »

that it may be but it still has to be either legal or not...

I would say since it is not illegal, then it is legal - that is my logic anyway.
I personally don't expect every single aspect of my life, driving, working etc to be described legal/illegal.
For example: (extreme example)
It is not illegal to wear tshirt when outside temp is 2 degrees, it is legal then, but does legality of it make it less stupid?
Yes, you can walk in one shoe only, it is perfectly legal. It is pointless, and uncomfortable tough...

So coasting is not described legal/illegal, but is kind of pointless too. There is no need to look for it in any book, (Cinio will try anyway). What driving instructors are saying about it is right, and since all current cars have MPI engines, and nice and smooth gear change, there is no need to crawl along downhill in neutral. There are some safety issues with it too.

Neilw

I was in China for a few weeks and noticed coasting was common practice, any car I was in the driver would coast it along. They accelerate to speed, then coast in nutral until the car slows down then repeat. Even busses and coaches were doing it

Gumbo

challengemaster wrote: »

I'd love to see the law on that one

CiniO wrote: »

Links please...

Maybe this is a classic example of how something is drilled into you when learning that you took it as gospel Although i learned to drive in different times to the present system so all theat BS may be out of the system by now.

Also there may be some mix up as to what the term coasting means, ie. just letting the car free roll while still turned on or turning the engine off and rolling down a hill for example.

shedweller wrote: »

As is going over 120kph on the motorway but i don't see anyone complaining about that.

hang around here long enough and you soon will

johnayo

Cookie_Monster wrote: »

in a modern car, no. if in neutral the engine needs to be fed petrol to tick over. if a gear is engaged the motion of the car keep the engine turning and no petrol is allowed into the cylinders saving fuel

If no fuel was allowed into the cylinders then the engine would surely cut out.
This is only relevant on cars that have stop-start systems.

piston

How on earth can it be illegal? There have been cars such as some Rovers and and all Saabs of a certain age that have a bicycle style freewheel mechanism. If coasting was illegal, by definition, these cars would never have been allowed on the roads.

Quazzie

johnayo wrote: »

If no fuel was allowed into the cylinders then the engine would surely cut out.
This is only relevant on cars that have stop-start systems.

The momentum of the car keeps it going, and the car diesels with no fuel being used.

johnayo

Quazzie wrote: »

The momentum of the car keeps it going, and the car diesels with no fuel being used.

Does this mean the engine is not running then.

lkdsl

The original question was about coasting - in modern diesel cars you will use less fuel with the car in an appropriate gear and no pressure on the accelerator. This obviously only works downhill or when you want to slow down. Putting the car in neutral (what is being described above) uses more fuel (on the cars I have tried it on). I've no idea why! It may have something to do with the electrical system re-capturing some of the energy - a technique that is a common fuel saving technique in modern engines.

When I learnt to drive (a long time ago) I was taught not to put the car in neutral so that I had immediate control of acceleration/deceleration if required.

Quazzie

johnayo wrote: »

Does this mean the engine is not running then.

When the car is in motion and you take your foot off the accelerator, the electronics ensure that a small amount of fuel is injected into the engine, to to keep the combustion process going. If the car is moving and in gear, the momentum of the car runs the engine as opposed to the opposite which is normal. The fuel used during this process is minuscule and whilst its technically using some fuel it in negligible.

When a car is coasting it is like the car is standing still in neutral and a lot more fuel is required to keep the car running at 700-800 RPM than is need to ensure combustion.

tuxy

Quazzie wrote: »

When a car is coasting it is like the car is standing still in neutral and a lot more fuel is required to keep the car running at 700-800 RPM than is need to ensure combustion.

That's why you should switch your engine off before going down a big hill. Just watch out for the wheel lock

Quazzie

tuxy wrote: »

That's why you should switch your engine off before going down a big hill. Just watch out for the wheel lock

Close your eyes for extra lulz

piston

I remember my dad having a MK4 Cortina back in the day. For whatever reason, the steering lock didn't work on that car. We lived at the bottom of a steep hill and he used to switch the engine off at the top of the hill and coast down it and down the driveway. When he replaced the car with a newer Cortina, the first time out, he switched the engine of as usual and when he went to turn down the drive, the steering locked and we hit the pillar

Where To

piston wrote: »

I remember my dad having a MK4 Cortina back in the day. For whatever reason, the steering lock didn't work on that car. We lived at the bottom of a steep hill and he used to switch the engine off at the top of the hill and coast down it and down the driveway. When he replaced the car with a newer Cortina, the first time out, he switched the engine of as usual and when he went to turn down the drive, the steering locked and we hit the pillar

Careful now!
A man down the pub told me it was illegal todrive with a broken steering lock :P